The need for censorship of video material is generally accepted by most societies, for the purposes of preventing the viewing of material by persons other than the target audience. Usually, such censorship takes the form of limiting access of a certain group of people, for example children, to a certain class of material, for example pornographic or violent movies. Other uses of censorship include voluntary self-censorship in cases where a recipient of a program does not wish to be exposed to certain types of program, for example scenes of great violence or advertisements which may be considered offensive by some people.
Being the most widely distributed form of broadcasting, television is the medium in which censorship is most likely to be considered a problem. Traditionally, censorship of television takes the form of either preventing possibly offensive material from being broadcast in the first place, or voluntary self-censorship, that is, switching off the receiver when material which the viewer does not wish to experience is being broadcast. While such self-censorship offers the benefit that programs remain available to those who do not find them objectionable, it suffers from the inconvenience of having to anticipate the nature of broadcasts and operate the receiver appropriately. This process is tedious and error-prone, especially where the viewer wishes to suppress program material which changes rapidly in nature, for example when the viewer desires to suppress commercial messages within an otherwise unobjectionable program. Manual censorship is therefore not an entirely satisfactory solution.
Another factor which renders manual censorship ineffective is the increasingly common use of videotape recorders for recording programs for later replay. If an operator is present at the time of recording, unwanted program can be suppressed by "pausing" the video recorder when appropriate, but in many cases such recording takes place unattended and at these times such manual censorship is not possible.
It is therefore desirable to provide means whereby display or recording of preselected classes of program material can be automatically suppressed.
Arrangements for automatic censorship have been previously published, but suffer from a number of serious shortcomings. The main difficulty is that automatic means for recognising different program classifications, for example detection of television commercials, have been complex and unreliable. One technique has been to detect television commercials by the short period of black picture and silence separating them from other program material. A typical commercial-deleter of this type is disclosed in U.S. Pat. No. 4,319,286. This system and others like it suffer from the problem that erroneous operation occurs if there is a brief period of black and silence in a broadcast at a time other than at the beginning of a commercial break, or if there is no separation between commercials and other program material. Furthermore, such systems are unable to distinguish between resumption of desired program and further commercials at the conclusion of a commercial. Resumption of viewing or recording must therefore be controlled by some form of timing device, based on assumptions regarding the length of commercial breaks. If these assumptions are not correct, the system will fail in its function.
A much improved censorship means is disclosed by Von Kohorn in U.S. Pat. No. 4,520,404. This system relies on a human operator to classify broadcasts, based on observation at a monitoring station. A suitably coded message is distributed from the monitoring station to the viewer's home, at which point a suitably-equipped decoder controls the television receiver or video recorder in accordance with the classification data generated by the human operator at the monitoring station. Although this invention significantly improves upon the reliability of previous methods, it nevertheless suffers from a number of significant limitations.
The main limitation of the prior art arises from the means of distribution of classification data to the viewer's home. In the Von Kohorn patent cited above, the system relies on a special-purpose radio broadcast, a special-purpose cable connection or specially-encoded control signals accompanying the broadcast to be censored as the means of distribution of classification data. The provision of special purpose radio broadcasts presents the problems of cost and complexity of establishing suitable transmitters, which must be capable of delivering suitable signals to all users of the service, as well as the difficulty and expense of obtaining such license as may be required by communications authorities. Distribution by cable suffers from the high cost of establishing of suitable cabling, or difficulty of securing a suitable channel within a cable network already in place. Distribution by means of encoded signals accompanying the subject broadcasts is difficult to achieve as it requires the cooperation of the broadcasters.